1. Field of the Invention
The present invention relates to a method of sterilizing an intraocular lens, which method permits the intraocular lens to be sterilized in a short period of time in a simplified manner.
2. Discussion of the Related Art
Intraocular lenses have been used in cataract surgery. Namely, the intraocular lens is implanted in a human eye from which a crystalline lens has been removed in the cataract surgery. The intraocular lens includes an optical portion which serves as an optical lens to give a desired eyesight, and a support portion which holds the optical portion in position within the eye. As examples of such an intraocular lens, there are known a one-piece type intraocular lens in which the optical portion and the support portion are integrally formed of the same material, and a separate-piece type intraocular lens in which the optical portion and the support portion formed of respective different materials are assembled together. The optical and support portions of the intraocular lens are formed of a homopolymer or a copolymer of alkyl(meth)acrylate such as methyl methacrylate, or a silicone resin, for instance.
The intraocular lens which is implanted in the eye needs to be sterilized by a suitable sterilizing treatment after the intraocular lens is formed of a predetermined polymer. To this end, the intraocular lens is usually subjected to a sterilizing treatment using an ethylene oxide gas (hereinafter referred to as "EOG"), by taking account of the low heat-resistance of the intraocular lens. The sterilizing treatment using the EOG, however, causes various problems as described below.
By taking account of a possibility that the intraocular lens is contaminated with microorganisms after the sterilizing treatment, the intraocular lens is subjected to the sterilizing treatment while it is accommodated in a sterilizing bag formed of a suitable material which inhibits entry of the microorganisms. In other words, when the intraocular lens is sterilized by using the EOG, the intraocular lens must be accommodated in the sterilizing bag formed of a suitable gas-permeable material which permits transmission of the EOG therethrough. However, such a gas-permeable material is limited, and therefore the sterilizing bag formed of the material which permits the permeation of the EOG therethrough but inhibits the entry of the microorganisms thereinto undesirably tends to be very expensive.
Further, the use of the EOG gives rise to environmental pollution because of its toxicity. In addition, the intraocular lens which was sterilized by using the EOG must be subjected to aeration operation for a relatively long period of time for the purpose of removing the EOG, since the EOG which remains in the sterilizing bag is harmful.
Moreover, the sterilizing treatment using the EOG needs to be effected while accurately controlling the sterilizing conditions such as the temperature, humidity and concentration of the EOG, and inevitably requires an expensive sterilizing equipment. In addition, the EOG-sterilized intraocular lens must be subjected to a sterility test which lasts for at least 14 days. This is an obstacle to expeditious shipment or delivery of the product (intraocular lens), pushing up the cost of the intraocular lens.
Instead of using the EOG for sterilizing the intraocular lens, it is proposed to use gamma (.gamma.) rays ("Eur. J. Implant Ref. Surg.", Vol. 1, March 1989, p.55-57). However, this method suffers from various problems. For instance, this method requires several hours, specifically, about 8 hours for completing the sterilization of the intraocular lens. Further, the material of the intraocular lens may be deteriorated due to reaction of the gamma irradiation and oxygen in the atmosphere or oxygen contained in the lens material. The degree of deterioration of the lens material will increase with an increase in the time period required for the sterilization treatment. In addition, it is troublesome to dispose of the radioactive material which was used for generating the gamma rays.